On RHL 8, if both sendmail and postfix are installed,
$ man sendmail
pulls up the Postfix sendmail man page, even when alternatives has sendmail
configured as the preferred MTA.
The basic problem is that Postfix supplies /usr/share/man/man1/sendmail.1.gz,
while Sendmail supplies /usr/share/man/man8/sendmail.8.gz; since section 1 is
before section 8 in the man section search path, the Postfix man page comes up
instead of the Sendmail man page.
Ideally, alternatives would correct for this, perhaps by something like:
sendmail supplies /usr/share/man/man8/sendmail.sendmail.8.gz
postfix supplies /usr/share/man/man1/sendmail.postfix.1.gz
alternatives creates /usr/share/man/man1/sendmail.1.gz ->
/usr/share/man/man1/sendmail.postfix.1.gz symlink if Postfix is the preferred
MTA, and creates /usr/share/man/man8/sendmail.8.gz ->
/usr/share/man/man8/sendmail.sendmail.8.gz symlink if Sendmail is the preferred MTA
(obviously, this requires fixes to the postfix rpm as well, but bugzilla won't
let me file the same bug against two packages)

I added this to the postfix spec:
--slave %{_mandir}/man8/sendmail.8.gz mta-sendmailman
%{_mandir}/man1/sendmail.1.gz \
I think you'll need to add this to the sendmail spec:
--slave %{_mandir}/man8/sendmail.8.gz mta-sendmailman
%{_mandir}/man8/sendmail.8.gz \
I don't think you need to rename the man page to append ".sendmail"
because the sendmail and postfix versions of the man page live in
different directories and hence have unique paths. I do realize that
when linked via alternatives this will cause the postfix version of
the sendmail man page which by default lives in section 8 to display
with section 1 in the title, but I'm not losing sleep over this :-)
I'm assigning this to you Thomas so you can update sendmail.spec.

This is not the correct solution. If sendmail asns postfix are both
installed and you are calling man sendmail you are netting the '
Postfix to Sendmail compatibility interface' man page regadless if you
are using postfix or sendmail as mta. This is a big problem. If you
call man, it finds the man page in man1 prior to man8.
The correct solution is to rename %{_mandir}/man1/sendmail.1.gz to
%{_mandir}/man1/sendmail.1.gz.postfix and to put it in alternatives.
By the way: This problem still occurs on fc2 with postfix-2.0.16-13.

Good catch Thomas! O.K. this is what I did:
--slave %{_mandir}/man8/sendmail.8.gz mta-sendmailman
%{_mandir}/man1/sendmail.postfix.1.gz
note that both sendmail's and postfix's man page will point to whats
in man8 now. You will have to add this to sendmail's alternatives
otherwise there is going to be a collision on
/usr/share/man/man8/sendmail.8.gz.
This change first appears in postfix-2.0.18-2 which is currently
building in dist-fc2.